High frequency amplifier circuits



March 30, 1943.

M. J, o. STRUTT ET AL HIGH FREQUENCY AMPLIFIER CIRCUITS Filed May 3, 1940 M m U 0 8 Z Wm T s m RmZ Y m m m many v v N m WNW A MTfi um m m IL MA 4 "m 1/ 9O [-2 7 9 2 .8 H; I 1 u! rflmw r.. i. 3 T Wu A V F 4 ,1 fl

SOURCE OF INEUZ Y VOLTAQE cathode being provided with one of which is included in the control grid cirtwoleads. one of which is included in the grid circuit and. another in the anode circuit In this case'the'input damping which is ,due to 1othei 'fcauses, for example the time oi'j' mately proportional to the squared the frequency, and consequently increases rapidly with should besuppressed or-even 2 used; ;for entirely, tarmac,

vand nineamping of'theim Patented Mar. I 30,

UNITED STATES PATENT OFFIC 'HIGH FREQUENCY AMPLIFIER CIRCUITS Max imiliaan mu om strutt and 4mm van der-Ziei, Eindhoven, Netherlands, assignors to Radio Corporation Delaware Application May 3,1910, Serial No. 3 In the Netherlands Jul, 25, 1939 of America, a corporation of .2 Claims. (01. 179-171) This invention relates to circuit arrangements for amplifying electric oscillation, use being made of an electron discharge tube having at least a cathode, a control grid and an anode, and the at least two leads,-

cult and another in the anode circuit. f

It is a well known phenomenon, whichstandsout particularly in the amplification of very short waves, that the cathode lead of a high frequency amplifier tube can bring about substantial damping of the input circuit due'to the fact that the impedance of the cathode lead is common for L the grid and anode circuits. It is, also, known that this damping eil'ect of the cathodelead can be avoided by providing the cathode with at least control particularlyimportant with short waves is maintained, finite transit This damping isapproiiieelectrons.

shorter waves. 'For this reason itisiinsufiicient desirable that the entire damping Y H M mad'e'negativerand in this-lattencase the; negative' dampingi can be c pensat n the damping: due "to thefpreceding amplifier tube mire sac-mputkte tma s v y c to: t e r eati i v mi isx result connected oscillations to be amplified; to the lead thecontrol grid 3 and the point embodiment of the invention. Figs. 2 and 3 show modifications. 1

Referring now to Fig. 1-, numeral I designates an amplifier tube comprising a cathode 2, a c ntrol grid 3, auxiliary electrodes 4 to Ban an anode I. The cathode is provided with two leads having-included in them impedances' shown in this figure as inductances L1 and L2. Between 8-of the cathode which is connected to the cathode lead included in the control grid circuit there is a capacity C1. Between the control grid 8 and the point 9 of the cathode lead, included in the anode circuit that .is-notconnected to the cathode, there is a capacity 0:. Vi designates'the input voltage-to be amplified which is supplied between the input ter- II and H. For the sake of simplicity the input and output circuits themselves and the supply sources of direct current are not shown.

For the most general case we assume that the tube I contains a secondary emission cathode having a mutual conductance of the secondary emission current going to the anode as a function 01' the control grid voltage equal to -81; and that this auxiliary cathode is connected, for the put circuit. The cases where an auxiliary cathode is notpresentcan be derived from the general is obtained w th tubes hag'ifiaat least. two cathode the fact that between the control grid and the i point of'fthe cathode which is connected to the cathode lead included in the control grid circuit and between thecontrol grid and that point of legdsiorieor mcn.i nclficd in'the control grid 'circuit' ahd another in the -anod'e circuit, due to pedances'being such that the damping between the input terminals 01' the discharge tube is substantially zero or negative.

' In. order that the invention derstood and readily carried into eifect it will now be described more fully with reference to the ac- "companying drawing in which Fig. 1 shows one maybe clearly unfa l a e which are'fmh fcm toj minus: are discounted.

. ing of the impedances included case by 8i to beequal to 'z'ero.\

will. he termed t the mutual concathode currentas a function gflri'yoltage. 'be termed Sr, In "C h x ntro .iii-a ai tcar c ty nd in C2 betwe n ilie cqritrcl grid a d; the sir-electrodes, and the anode It is assume nature miitual conductance of the i auxiliary 'electrodesconnectedto Ofis negligible;

Now, theiinvention makes available the fact that between'the admittance Yo w'hichoccurs between the input terminals l0 and .II of the discharge tube and the values w, Sh, Sr, L1, L2, 01'

and C2 the following relationship exists:

to the m-.

The angular irequency of theoscillations to be I This impedance is negative, and can be used with ing the damping due to the transit time of the electrons, and in addition the damping due to the preceding amplifier tube, and/or the dampbetween the input terminals Ill and I I mgince the damping of the input circuit is approximately also proportional ductance Sr.

to c this compensation is secured to a large frequency range.

In practice the most simple case in this respect is where a tube does not contain a secondary emission cathode so that --Sn=0, and in this case the admittance In this case the inductance of the cathode lead 8- -li and also the value or the capacity C1 is immaterial and thus the damping reducing effect is practically only governed by the inductance L2 and the capacity C: and also by the mutual congrid capacity in the case of a triode and the anode-control grid screen grid-control grid capacity (approximately therefore the screen grid-control grid capacity) in the case of a tetrode, 'and so forth, without there being supplementary capacities deliberately provided.

According to the invention, in this case the value of In must be such in connection with the The capacity C2 may be the anodeductances can obviously be increased artificially in order to obtain the desired efiect. By comparing formula (1) with formula (2) it is evident that in the use of a secondary emission tube, due to themutual conductance of the secondary emission current, the same means permit of obtaining an appreciably higher damping-reducing effect than with a tube without such an auxiliary cathode. In the circuits shown the two cathode leads are always connected to different sides of the cathode. sential, but thetwo leads may also be connected, 'ior example in common, to one point of the cathode. It is, also, obvious that the invention can be used without difliculty for tubes comprising three or more cathode leads, and in this case, for example in the event of three cathode supply conductors, the third one is used for other purposes.

What is claimed is: 1. A circuit for ,the amplification of high frequencies, comprising aneiectron discharge tube values of the capacity 02 and of S: that the damping reducing eflect according to formula (2) is equal to, erexceeds, the damping due to the transit time of the electrons. Such a circuit arrangement is shown in Fig. 2 in which Ca represents a filter condenser.

Alternatively, it may be assumed that In represents the inductance of the lead and according to the invention it is in this case necessary for C: to beincreased by means of supplementary capacities in such manner that the value of Yo according to formula (2) is equal to, or-exceeds. the damping due to the transit time of the electrons. According to formula (1), ii the tube is provided with a secondary emission cathode the inductance L1 and the capacity C1 deploy a part so that this should be taken into account.

tube of this kind is diagrammatically shownin Fig. 3, the same numerals designating corre .sponding parts of Figs. 1 and 2. In addition, I!

designates the source oi supply voltage for the secondary emission cathode i. In this case (see also Fig. 2) C]. may be. ior. example, the control gridrcathode capacity and C: the screening gridties being deliberately provided. Accordinrto the invention, in this case L1 and L2 respectively may be such that according to formula (1) 10' is equal to, or exceeds, the damping due to the finite transit time of the electrons, As before,

the inductances of the cathode leads themselves may be chosen to constitute Li and 1a and in this case the capacities-C1 and/or C: are incontrol grid capacity without any other capaciprovided with atv least a cathode having two external terminals, a signal input grid and an anode, the cathode having a lead connected to each of its externalterminals, input and output circuits connected respectively to the input grid and to the anode. the grid return of the input circuit being connected to one o! the cathode leads, the plate return of the output circuit being connected to the other cathode lead, a condenser connected from the signal input grid to a point having the same radio frequency potential as said plate return, and an inductance included in the cathode lead to which the plate return is connected, the condenser and inductance being chosen of such value that damping between the terminals of the input circuit is substantially zero. I

2. A circuit for the amplification of high frequencies, comprising an electron discharge tube provided with at least a cathode having two external terminals, a signal input grid and an anode, the cathode having a lead connected to each of its external terminals, input and output circuits connected respectively to the irput grid and to the. anode, the grid return of the input circuit being connected to one of the cathode leads, the plate return of the output circuit being connected to the other cathode lead, an inductance included in the latter cathode lead, and a condenser between the control grid and the end of said inductance remote from said cathode, the product of the values of said increased in such manner by deliberately provided supplementary capacities that the desired effect according to the invention is obtained.

In both cases the capacities as well as the inductance and condenser being sufllciently great that pcsitive'condu'ctance is eliminated from the input admittance of said tube,

MAXIMILIAA JULIUS OTTO STRU'I'I. ALBERT VAN on ZIEL.

This is, however, not es-. 

